Colour photography

ABSTRACT

A process for the manufacture of screened coloured positive direct-viewing images, for rapidly recognising in the printing industry the matching of the separation negatives which the final printed product will display, is described.

United States Patent [191 Kirsch Nov. 13, 1973 COLOUR PHOTOGRAPHY [56] References Cited [75] Inventor: Hans-Rudolf Kirsch, Zofingen, UNITED STATES PATENTS Switzerland 3,576,627 4/1971 Kuho Wirth 96/23 [73] Assignee: Ciba-Geigy AG, Basel, Switzerland Primary Examiner-Norman G. Torchin [22] Flled July 1971 Assistant Examiner-Alfonso T. Suro Pico [21] Appl. No.: 163,496 Attorney-Harry Goldsmith et al.

[30] Foreign Application Priority Data [57] ABSTRACT July 24, 1970 Switzerland 11292/70 A process fo the manufacture of screened coloured positive direct-viewing images, for rapidly recognising [52] US. Cl 96/30, 96/23, 96/4 in the printing industry the matching of the separation [51] Int. Cl G03c G030 5/44, G03 negatives which the final printed product will display, [58] Field of Search 96/1 1, 16, 23, 38, i d ib d 4 Claims, N0 Drawings COLOUR PHOTOGRAPHY The present invention relates to a process for the manufacture of screened coloured positive directviewing images, which in the printing industry make it possible rapidly to recognise the matching of the separation negatives which the final printed product will display. The colour shades of the prime colours yellow, magenta and cyan are so controlled by the copying process that they are matched to the printing inks.

The proof printing of a photolithograph or half-tone print is today still a time-consuming and expensive matter. Various experiments have already been carried out in order more rapidly and more cheaply to produce sample prints which accord with the product from the printing machine, whilst eliminating the customary proof printing approach. Hitherto, however, the methods are expensive or the results too dissimilar to the printed product.

Special problems arise in the manufacture of socalled colour proofs on photographic multi-colour material because in the graphic trade it is required that a proofing system" should possess variability or adaptability of the prime colour shades and colour densities to the particular printed product.

A process has now been discovered which fulfils this requirement and yields images which come very close to the printed product.

Accordingly, the subject of the invention is a process for the manufacture of a screened photographic colour copy which simulates a multi-colour print, preferably a multi-colour offset print or letterpress print, in which the screened negative colour separations of the original which correspond to the individual colours, and optionally additionally the black separation, are individually and successively exposed onto a light-sensitive negative-positive-working photographic material, characterised in that at least one of the colour separations is additionally exposed onto the light-sensitive colourphotographic material using the copying light of a colour corresponding to a different colour separation, and that the material exposed in this way is processed to give a screened, positive direct-viewing image which shows prime colours which match the printing inks.

In the process according to the invention, the procedure followed is thus that the screened negative colour separations of the original (blue B, green G, red R, black S) are successively, in optional sequence and in register, individually exposed with the corresponding filters (blue b, green red r) onto a lighbsensitive negative-positive-working, colourphotographic material, B b, G g, R r and S with white light, the improved matching of the colour impression of the colour copy to the printing inks being achieved by additionally carrying out at least one of the following exposures: B g, B r, G b, G r, R b and R g.

The exposures of the colour separations and of the admixture are computed from the densitometric measurement of the printing inks and of the photographic copy.

In the process according to the invention, the procedure followed is thus that, depending on the measured colour deviation of the individual prime colours of the fcolour proof from the printing ink or printed p rod net, a second and, if appropriate, a third screened colour separation negative is individually exposed, to a greater or lesser extent, with the light of the first colour separation negative, this being done in such a way that the proportion of the exposure of the additional second or third colour separation is as a rule 10 to 100 percent, preferably 20 to percent, of the exposure time of the first colour separation, that is to say the exposure times are in the ratio of 1:10 to 1:1, or 1:5 to 121.4. The matching of the individual prime colours of the colour proof to the printing conditions is achieved by lesser or greater exposure of the colour separations.

The black separation can be exposed in two ways. In the first, simple method exposure is carried out with white light, without a filter. Here, the black shade can vary, depending on the colour material used. In the sec- .ond method, the shade can be influenced. This requires three exposures with the primary colours blue, green and red, and the black shade can be changed through the amount of light for each filter.

All substractive colour materials are in principle suitable for this process, but photographic silver dye bleach material, which can for example be processed according to British Patent Specification No. 967,036, is preferred.

The colour separations required for the process according to the invention, for example the green, red

and blue filter separation, as well as the black separation, are produced in the customary and known manner. Since these screened separations are in the form of monochromes, and generally black-and-white, screened negatives, the choice of the copying lights in the further photographic processing only still depends on the spectral sensitivities of the copying material.

The mostly black-and-white screened colour separation negatives correspond to the negatives usually employed in screened offset and letterpress printing technology. These screened negatives have as a rule been produced as direct screened separations by means of gravure or contact screens from colour direct-viewing originals and colour diapositives, either conventionally by means of a reproduction camera or an enlarger, or via so-called scanners." The colour retouching and correction of the colour separations is matched to the works colour scale of the individual printing works.

EXAMPLE 1 If, when printing, a warmer magenta colour is printed than that of the colour proof", the colour proof" can be matched to the printing ink by increasing the proportion of yellow in the magenta. The procedure is as follows:

Using a registering device, the screened negatives are individually copied onto a negative-positive-working photographic silver dye bleach material. First, the blue filter negative is copied with blue light, and then the green filter negative for the mixed exposure (30 percent of the blue filter negative exposure) is copied. Thereafter, the green filter negative is exposed with green light, the red filter negative is exposed with red light, the black print negative is exposed with white light. After these five exposures, the colourphotographic material is developed to give a positive direct-viewing image which comes close to the printed product manufactured with the same separations.

1. Blue filter negative Blue exposure Blue exposure 2. (ireen filter negative Total 3. Green filter negative l-- Green exposure 4. Red filter negative Red exposure White exposure 5. Black print negative For comparison, the printing ink and the photographic colour proof are measured without and with admixture of a second or third colour separation.

The following values are found:

Relative densities Measuring filter exposure O ative, behind a grey density of 0.6, is 3 seconds I I: Densities of the printing ink used.

II: Densities of the colour proof" without admixture. III: Admixture of yellow to magenta. The blue exposure with the green filter negative is 30 percent of the blue exposure with the blue filter negative.

EXAMPLE 2 If warmer magenta and cyan printing inks are used than in the colour proof", the procedure for adapting the colour proof is the following:

percent, that for the green filter negative is 0.9 second (=30 percent) and that for the red filter negative is 0.9 second 30 percent). As a fourth exposure, the green filter negative is copied with green light (7.7 seconds behind a grey density of 0.3), and as a fifth exposure the red filter negative is copied with red light (1.9 seconds behind a grey density of 0.3). As a sixth exposure, the black print negative is additionally exposed with white light (3 seconds behind a grey density of 0.9). After the exposures and the development a positive direct-viewing image is obtained, which comes close to the printed product produced with the same separations.

RELATIVE DENSITIES Relative densities Measuring filter Total exposure EXAMPLE 3 If purer printing inks are used, that is to say printing inks with lesser subsidiary colour densities, the colour proof must also be produced with purer colours. In this case, instead of using a chromogenic colourphotographic material, a material based on the'silver dye bleach process is used.

The procedure is as represented in Example 1, except that the green filter negative exposure with blue light is 60 percent of the blue filter negative exposure. The resulting colour correction is shown by the following data:

Relative densities Measuring filter exposure.

It can be seen that the densities of the corrected colour proof" agree very well with those of the print.

I claim:

1. Process for the manufacture of a screened photographic colour copy simulating a multi-colour print, in which the screened negative colour separations of the original which correspond to the individual colours, and optionally additionally the black separation, are individually and successively exposed using their corresponding copying color light onto a light-sensitive negative-positive-working substractive photographic material, which comprises additionally exposing at least one of said screened negative colour separations onto the light-sensitive colour-photographic material using the copying light of at least one of the other color separations and processing the material exposed in this way to give a screened, positive direct-viewing image which shows prime colours which match the printing inks.

2. Process according to claim 1, wherein the exposure times of the colour separations exposed with copying light of the same colour are in the ratio of between 1:10 and 1:1.

3. Process according to claim 2, wherein the exposure times of the colour separations exposed with copying light of the same colour are in the ratio of between 1:5 to 1:1.4'

4. Process according to claim 1, which comprises using a photographic material for the silver dye bleach process as the colour-photographic material. 

2. Process according to claim 1, wherein the exposure times of the colour separations exposed with copying light of the same colour are in the ratio of between 1:10 and 1:1.
 3. Process according to claim 2, wherein the exposure times of the colour separations exposed with copying light of the same colour are in the ratio of between 1:5 to 1:1.4.
 4. Process according to claim 1, which comprises using a photographic material for the silver dye bleach process as the colour-photographic material. 